Prefer matching llvm-config in find-llvm-config

[straight-shoota]

Even if the command llvm-config exists and its version matches, any other llvm-config* command with the same version would currently be preferred. That was unexpected for me.
I think it makes sense that llvm-config has preference.
For example, if you have both llvm-config and llvm-config14 in your path, the results would be llvm-config14 in master and llvm-config with this patch.

[sdogruyol]

Thank you @straight-shoota 🙏